Method and means for preheating electric accumulators such as lead-acid storage batteries

ABSTRACT

Storage batteries, particularly those of the lead-acid type, are preheated electrically by subjecting the electrode plates of the battery to an inductive alternating field which induces electric current in the plates. The frequency of the inductive field preferably is within the range from about 250 Hz. to 1,500 Hz. The intensity of the field is reduced or the heating field is terminated upon a sufficient rise in plate temperature.

United States Patent Brinkmann et ai.

[54] METHOD AND MEANS FOR PREHEATING ELECTRIC ACCUMULATORS SUCH AS LEAD-ACID STORAGE BATTERIES of Berenbostel, Germany Varta Aktiengeselischait,Frankfurt/Main, Germany Filed: Apr. 13, 1970 Appl. No.: 27,752

Assignee:

[30] Foreign Application Priority Data Apr. 12, 1969 Germany ..P 19 i8726.9

11.8. CI. ..219/209, 320/2 Int. Cl. ..H05b 1/00 Field oiSearch ..219/6,5, 209, 10.41, 10.43, 219/1047, 10.49, 10.51, 1057,1075; 136/161;320/35, 36, 2

Inventors: .1 iirgen Brinkmann; Wieland Gehrke,both

[is] 3,654,426 [4 1 Apr. 4, 1972 Rheinstahl Henschel A.G., 1,496,134,12/ 1 2/64,

Primary Examiner-C. L. Albritton Attorney-Curt M. Avery, Arthur E.Wilfond, Herbert L. Lerner and Daniel J. Tick [57] ABSTRACT Storagebatteries, particularly those of the lead-acid type, are preheatedelectrically by subjecting the electrode plates of the battery to aninductive alternating field which induces electric current in theplates. The frequency of the inductive field preferably is within therange from about 250 Hz. to 1,500 Hz. The intensity of the field isreduced or the heating field is terminated upon a suflicient rise inplate temperature.

22 Claims, 7 Drawing Figures INVERTER PATENTEDAPR 4 I972 SHEET 2 OF 2 DC/AC INVERTER FIG.6

METHOD AND MEANS FOR PREHEATING ELECTRIC ACCUMULATORS SUCH AS LEAD-ACIDSTORAGE BATTERIES Our invention relates to methods and means forpreheating electric accumulators of the type that exhibit optimumperformance within a given range of temperatures, this beingparticularly the case with lead-acid storage batteries. Morespecifically, the invention concerns a heating method and heating devicewhich effects the desired preheating by means of electrical current.

in a more particular aspect, the invention relates to storage batteriesconnected with or incorporated in the electric wiring system on anautomobile, boat or other automotive vehicle, especially vehiclesequipped with an internal combustion engine which drives adirect-current or alternating-current generator (alternator) forenergizing the electric system and in which the storage battery, chargedfrom the generator or alternator, serves to operate an electric motorfor starting the engine.

The power delivery and the power storage capacity of storage batteriesis greatly dependent upon temperature. At extremely low temperatures,even a fully charged storage battery may not be capable of furnishingthe power required for starting the engine of the vehicle. Since withincreasing temperature the required starting power decreases while thepower dischargeable from the battery increases, the starting performancecan be improved by preheating the driving assembly and the storagebattery. The' high-current capacity of storage batteries at lowtemperatures is particularly slight when the battery is only partiallycharged. Hence, to prevent starting trouble at low temperatures, thestorage battery must always be kept in good charged condition. Thiscalls for fastest feasible preheating of the battery when operating thevehicle so as to secure a high charging rate for a given constantcharging voltage. For vehicles equipped with devices that consumerelatively large amounts of electric energy, consuming load devices,such as window opening drives, heaters and air-conditioners, that mayoperate at standstill of the driving engine, it is desirable that duringthe next running periods of the engine the storage battery will reliablyreach the heated state at which it will again be charged as rapidly asfeasible.

Problems of this kind are particularly apt to occur with heavy militaryvehicles, for example with military tanks or the like armored vehicles,so that on such vehicles the batteries are often provided with means formaintaining them in heated condition.

Various battery heating methods have been proposed. For

example, it is known to provide for hot-air heating of a storage batterywith the aid of a flow of heated air which passes around the blockcontainer of the battery. The heat must penetrate through the blockcontainer into the interior of the battery. Thus the electrolyte at theinner surfaces of the battery container becomes heated first; andconvection or circulation of the acid in the container, caused by theresulting differences in density and by heat-conductance, then causesthe entire storage battery to be heated ultimately. For a giventemperature difference between the battery interior and the heating air,the temperature rise in the storage battery is substantially dependentupon the heat conductivity of the container material rather than uponthe heat transfer at the inner surface of the container wall. For thisreason, other heating media, for example heated water, applied underotherwise similar conditions, cannot appreciably increase the rate oftemperature change. In addition, when using water as heating medium, thepredetermined temperature difference, generally, is smaller than whenheated air is used because the water temperature must remain below theboiling point.

With any heating methods that require the heat to penetrate through theblock container into the interior, the efficiency of the heatingperformance is rather small because the difference in thermalresistivities causes the major portion of the heat quantity to dissipateinto the environment rather than reaching the interior of the battery.Furthermore, the individual cells of the battery have considerablydifferent external surfaces so that the heat transfer facescorrespondingly differ from one another. As a result, the outer or endcells of the storage battery, when being preheated in this manner,assume a higher temperature than the inner cells, which leads todifferent power storage capacities of the respective cells.

For shortening the preheating period of storage batteries it has beenproposed to intensively heat the armature components of the battery, forexample the cell connectors and the end poles so that the heat isconducted through the pole shanks into the interior of the battery.Despite the good heat conductivity of the lead material which forms theelectrode plates in a lead-acid type battery, the thermal resistance isvery large on account of the relatively slight heat-conducting crosssection and the long path length. Furthermore, with this heating methodthe heat is first issued to the planar layers of the electrolyte in thestorage cell so that a natural circulatory motion of the electrolyte isnot effected to an appreciable extent. That is, the heat must bepredominantly transported by conductance to the lower zones of thebattery. Besides, the temperature up to which the armature componentscan be heated must not exceed a given, rather low limit because theconnectors and the pole lead-ins are arranged in a fusible casting massof low maximum permissible temperature.

According to another proposal, the storage battery is heated directly bypassing therethrough an electric current of medium frequency. The lossesoccurring in the internal resistances then cause preheating of thebattery. Since the internal resistances of the battery are slight, aneffective heating in this manner requires applying a very high currentof low voltage. This not only calls for unfavorably large cross sectionsof the electrical supply leads, but the development of heat is largelysituated within the electrolyte while the plates of the battery remainrelatively cold. Furthermore, the internal resistance of the batterydeclines with increasing temperature so that the medium-frequencycurrent passing through the battery increases steeply as the heatingtime progresses. This method also poses the danger that the storagebattery may discharge through the relatively slight internal resistanceof the alternating-current generator, so that it is necessary to provideadditional capacitors or, since capacitors for high current intensitiesare too large and too expensive, the battery must be subdivided intogroups to be fed with alternating heating current in a series-opposedcircuit connection. With this heating method, it is not possible tosimultaneously charge or discharge a storage battery since highalternating voltages are impressed upon its terminals during the heatingperiod.

In the above-mentioned circuit arrangement of capacitors, thesecapacitors prevent the flow of the direct current. When subdividing thestorage battery into groups, it is necessary to change the circuitconnection of the groups upon termination of the preheating period, or aportion of the groups can be discharged only through the internalresistance of the alternating current generator. This results in anasymmetry of the individual battery groups and also impairs thecurrent-voltage characteristic of the battery, which is disadvantageousparticularly to the engine-starting performance.

it is an object of our invention to minimize or eliminate theabove-mentioned disadvantages and shortcomings of the known methods andmeans for preheating of storage batteries.

More specifically, it is an object of our invention to devise a methodand means which afford preheating the storage battery in shortestfeasible time to such an extent that a good power delivering capacityand thereby a satisfactory enginestarting performance or an improvedpower storing ability are achieved.

Another object of the invention, in conjunction with those mentioned, isto afford readily charging or discharging a storage battery during theheating operation.

To achieve these objects and the further objects apparent from thefollowing, and in accordance with a feature of our invention, we effectthe preheating of storage batteries by subjecting the electrode platesof the battery to an alternating inductive field, thus inducing electricheating currents directly in the electrode plates of the battery.

Accordingly, we provide a battery container or holder structure with aninductive excitation or primary winding which extends about the storagebattery and is so situated that the electrode plate structures,preferably the grid structures of the lead plates in a lead-acid typebattery, constitute the secondary windings in which the currents,circulating within the respective plates, are induced.

As a result, the plate electrodes of the storage battery aresimultaneously heated to a substantially uniform extent, the lead gridsof the electrode plates acting as short-circuited windings in themagnetic alternating field of the primary winding. On account of theslight electrical resistances, the induced voltages producehigh-intensity currents well suitable to heat the grid structures of theplate. Thence, the heat passes to the active mass of the electrode plateand subsequently to the electrolyte contained in the pores of the mass.This heat transfer reflects but a slight jump in temperature, becausethe heat transfer surface between active mass and electrolyte within thepores is constituted by the very large totality of the pore surfaces. Inthis manner, the localities at which those electrochemical energyconversions take place that ultimately determine the power capacity ofthe storage battery, are intensively heated. This applies particularlyto the boundary faces between active mass and electrolyte. The acidbetween the plates, in the sludge space and above the sets of plates,will at first remain cold since the heat transfer from the active massand the acid in the pores to the other acid portions is relatively poor,having only the geometric surface of the plates available as heattransfer surface. However, the acid between the plates need notnecessarily be heated because the electrical conductivity of the acid atthis locality has no more than a negligible effect upon the electricaloperating qualities of the storage battery. As a consequence, thebattery electrically behaves as if it had a high temperature, althoughthe acid, in reality, exhibits a much lower temperature average value.The advantages of this type of heating resides particularly in the factthat the localities at which the charging and discharging ratedetermining reactions take place, these being critical to the powerstoring and delivering capacity of the battery, are directly heated andthat the specific heat of lead is only about 3 percent of the specificheat of the electrolyte. As a consequence, a storage battery can rapidlyand with a slight energy consumption be placed into a state of goodelectrical conduction ability.

The above-mentioned and other objects, advantages and features of ourinvention will be apparent from, and will be set forth in, the followingdescription of embodiments of the invention illustrated by way ofexample on the accompanying drawings, in which:

F IG. 1 is an explanatory diagram;

FIG. 2a and FIG. 2b show schematically the cover and the containerstructure of a battery equipped with induction heating means accordingto the invention;

FIG. 3 is a partial and sectional view of a similar container structure,also equipped with induction heating means;

FIG. 4 is another partial and sectional view of a different modificationof such a container structure equipped with induction heater means;

FIG. 5 is a schematic circuit diagram of a battery heating deviceaccording to the invention as part of the electrical system on anautomotive vehicle;

FIG. 6 is an electric circuit diagram of another electrical system ofwhich a battery heating device according to the invention forms part.

The coordinate diagram in FIG. 1 relates to the dischargingcharacteristic of heated and unheated lead-acid batteries having astorage capacity of 100 Ah (ampere hours) which were discharged by adischarge current of 300 A from a 100 percent charging capacity at thestart of the discharge. In the diagram, the abscissa denotes time (t)and the ordinate denotes voltage (V).

Curve 1 indicates the discharging characteristic of'a storage battery ata temperature of 40" C. This curve as well as all others are shown downto the final discharging voltage of 6 V.

Curve 2 shows the discharging characteristic at 20 C and curve 6 thecharacteristic at 0 C. Curves 3, 4 and 5 represent the dischargecharacteristics of inductively heated storage batteries at a dischargecurrent of 300 A. The heating frequency in these cases was about 900 Hz,the heating current was 30 A and the heating voltage 30 V. The startingtemperature of the heated batteries was at 40 C. For curve 3 the heatingperiod was 6 minutes, for curve 4 it was 9 minutes, and for curve 5 theheating lasted 15 minutes. It will be seen that by virtue of inductiveheating a considerably improved voltage characteristic and hence powerdelivery was obtained with a heating period of as little as 6 minutes(curve 3). With a heating period of only 9 minutes (curve 4) the batteryobtained a starting voltage (9, 5 V) virtually just as large as if thetemperature of the battery had been 20 C (curve 2). However, since withcurve 4 the final discharge voltage of 6 V was attained earlier thanwith curve 2, it will be recognized that the battery had the highertemperature of 20 C (as compared with 40 C) only at its activelocalities. Curve 5 relates to a heating period of 15 minutes. In thiscase, with respect to the starting voltage (near 10 V), the dischargecurve 6 for 0 C was almost reached and, with respect to the dischargingduration, the discharge curve for 20 C (curve 2) was already exceededalthough the battery during this short preheating period had not yetattained a median temperature of 20 C.

A variety of devices are applicable for performing the above-describedmethod according to the invention. In a particularly simple form, forexample, the battery to be heated is shoved into a ring coil to serve asthe primary winding of the induction heating system. Such an embodimentwill be more fully described hereinafter with reference to FIG. 6 whereeach battery B is inserted into one of the induction heater coils 51 to54. For reasons of space requirements, this type of device cannot alwaysbe employed. As a rule, therefore, it is preferable to arrange theprimary induction heater winding as represented in FIGS. 2a and 2b.

According to FIGS.2a and 2b, the primary winding is attached to theblock container 11 of the battery with the winding turns or portions sodistributed that there occurs a distributed winding 13 at the bottom andthe lateral walls of the battery container, whereas the winding 14 atthe upper edge of the block container is concentrated, i.e., the turnsor turn portions at this locality are more closely spaced from eachother. The cover 15 of the battery container is similarly provided atits surface with a distributed winding 16 and at the edges with aconcentrated winding 17. By such a distribution of the winding portions,a largely homogeneous field in the interior of the storage battery issecured. For obtaining a good magnetic flux path, it is preferable toplace flux guide sheets 18 around the winding. This reduces theexcitation power required for producing a given induction desired in theinterior of the battery; that is, the flux guide members 18 permitreducing the necessary amount of magnetic ampere turns. To attain aconcentration of the magnetic field in the area predetermined by thedimensions of the electrode plates, it is advisable to mount the fluxguide members 18 at about the same height as the electrode plates of thebattery and to arrange the flux-guide members approximately at theheight of the plates outside on the primary induction winding. This hasthe effect that the predominant portion of the magnetic field producedby the excitation winding will pass as useful flux through theelectrodeplate areas, thus securing an almost complete linkage of theflux between the secondary winding (electrode plates) and primarywinding. This serves to reduce the reactive-power demand and ultimatelyto increase the efficiency of the heating device.

As will be seen from FIG. 3, the inductive excitation winding 20 may bemounted directly on the block container 21 of the storage battery wherea winding is fixedly attached by a layer of plastic material 22 moldedor sprayed onto the container 21 which forms the electrolyte vesselproper of the battery. Flux-guide sheet member can also be fixed to thecontainer structure in this manner, as will be described with referenceto FIG. 4. After the plastic embedding material 22 (FIG. 3) is applied,a further box 23, made for example of glass-fiber-reinforced plastic, isplaced about the inner container structure and the remaining interspacebetween the outer box 33 and the inner container 21 is filled withheat-insulating plastic or other material, preferably a plastic foam.This increases the thermal time constant of the storage battery, thusretarding the cooling of the battery. The additional, external box 23can then be provided with supporting or fastening means such asexemplified at 25. According to another embodiment of the invention, aseparate box structure is employed for accommodating the inductiveexcitation winding and the flux-guide members. This box preferablycomprises an inner portion 32 of glass-fiber-reinforced plastic whichaccording to FIG. 4 surrounds the block container 31 proper and uponwhich the induction heater winding 33 and the flux-guide sheet members34 are arranged and fixed by a plastic material 35 in the mannerdescribed above with reference to FIG. 3. Thereafter, the inner portion32 with the winding and the flux-guide members is inserted into an outerportion 36 likewise preferably made of glass-fiber-reinforced plastic.The remaining interspace between inner portion 32 and outer portion 36is thereafter filled with plastic foam 37. As a result, there isproduced a composite box or holder structure into which the batterycontainer 31 proper is inserted and which secures high mechanicalstrength and good additional heat insulation. As explained, theinduction winding and the flux guiding members are embedded within thewall structure of the composite box.

To prevent excessively high temperature peaks in the containerstructure, as may be due to heat losses generated in the excitationwinding and to the heat insulation effected by the plastic foammaterial, it is preferable to coat the excitation winding and the fluxguiding sheet members, prior to entering the foam material, withheat-conducting graphite varnish or the like. The coating has the effectof uniformly distributing the heat generated in the excitation windingand to dissipate such heat predominantly through the interior of thecomposite box structure.

In some cases it is advisable to make the external wall portion of thebox structure of metal. For example, the box portion 36 in FIG. 4 may bemade of metal or, as shown, may be covered with a metal coating 38. Thiscompletely shields the magnetic field in the interior of the storagebattery from the environment. By employing magnetically conductingmaterial for or at the outer portion of the box structure, theflux-guide sheet members, or at least some of them, may be omittedbecause the external metal of the box structure also performs thepurpose of a magnetic yoke or flux guide. Space limitations may make itadvisable to omit the cover 5 (FIG. 2a). Then the storage battery ispreheated only by means of the excitation windings 3 and 4 (or or 33)accommodated within the container structure. This leads to a slightreduction in heating intensity, but the advantages of reduced spacerequirements and smaller weight of the container structure may outweighthis disadvantage in many cases.

A further embodiment results by accommodating the excitation winding andthe flux-guide members directly in the structures of the blockcontainers themselves. This is advantageous especially with blockcontainers of plastic material. In such cases it is advisable to placethe complete excitation winding and any flux-guide members into theinjection mold for the block container and to thereafter inject theplastic material into the mold so that the winding and, as the case maybe, the flux-guide members become embedded in the plastic material ofthe container structure.

The energy supply to the inductive heating means according to theinvention can be effected in various ways. One way is to connect theinductive heater winding to the three-phase alternator A (FIG. 5) of thevehicle and to connect the inductive heating windings, shown onlyschematically at 3, 4 and 6, 7 in FIG. 5, directly to the outputterminals R, S, T of the threephase alternator winding ahead of therectifier diodes 40 of the static inverter which furnish at terminals Pand N the direct voltage needed for the lamps and other devices to beenergized by direct current aboard the vehicle. The inductive heatingdevice for the battery B in such a system is energized at a varyingfrequency, namely the one furnished by the alternator A in accordancewith the rotating speed of the driving engine. If desired, however, anauxiliary generator or alternator may be used for supplying theinductive heating windings with energy independent of the engine speed.

Still another way is to connect the inductive heater windings to thedirect-current wiring system of the vehicle through a static inverter(direct-current to altemating-current converter) as shown at 55 in FIG.6. When the inductive heating device is connected to the three-phasealternator of the vehicle (FIG. 5) the heating of the storage batterycan be effected only when the engine is running. This, however, affordsthe assurance that due to the rapid improvement in current storingcapacity of the battery, the latter will always remain in a goodcharging state and for that reason, after cooling to ambienttemperature, can furnish a higher cold starting power than when inpoorly charged state under otherwise the same conditions. When a vehiclethus equipped and having an always well-charged battery remains atstandstill at low ambient temperatures, it is possible, for example, toemploy a small inverter to keep the battery by means of its own storedenergy on a desired temperature level during an additional prolongedperiod of time. Preferably, however, the preheating of the storagebattery, as a rule, is effected by connecting the induction heatingdevice to an auxiliary generator assembly or to a direct-currentgenerator G through a static inverter (55 in FIG. 6). In the lattercase, the energy for preheating may also be taken out of the batteryitself. This is so because the partial preheating and the slightspecific heat of the lead have the effect that in the region of lowtemperatures the electrical energy required for preheating is smallerthan the energy to be additionally taken out of the battery for thispurpose.

The frequency employed for inductive heating of batteries according tothe invention is preferably between about 250 Hz and 1,500 Hz, buthigher frequencies are also suitable. The particular frequency ispreferably chosen in dependence upon the construction of the storagebattery. When energizing the inductive heating device from the generatorused for lighting purposes on vehicles or from an auxiliary generator,it is in some cases preferable to connect capacitors such as shown at 45in FIG. 5 in series with, or parallel to, the excitation windings inorder to compensate some or all of the reactive power. By adding ordisconnecting a portion of the capacitors, for example with the aid ofswitches or relays such as shown at 42 in FIG. 5, the electricalimpedance of the circuit arrangement can be varied, thus also varyingthe power consumption of the inductive heating device for a givenconstant voltage. It is further possible to vary the frequency of theauxiliary generator or inverter, thereby also varying the powerconsumption of the inductive excitation winding due to the resultingvariation in impedance of the circuit arrangement. When energizing theinductive heater winding through a static inverter, a compensation ofthe reactive power of the excitation winding is not necessary if theinverter is provided with freewheeling diodes. In such cases, too, thepower consumption of the excitation winding can be varied by varying thefrequency and consequently the impedance of the inductive excitationwinding.

It will be understood that the heating of the storage cell can bereduced or terminated as the temperature of the electrode plate rises.For example, the intensity of the heating current can be reduced or theheating current discontinued manually when a given temperature isreached or simply when a given length of heating time has elapsed.However, the reduction in heating intensity or the switching-off of theinductive heater may also be effected automatically by sensing theelectrode temperature and controlling the heater current or itsfrequency in response to the sensor signal. Thus in FIG. 6 a sensor 57,such as a bimetal thermometer is shown placed upon a con- 7 nectorbetween electrode plates, the output signal being applied to a frequencycontrol 56 of the inverter 55 or simply to the desired reduction ordiscontinuance of the heating current when a given temperature isexceeded.

FIG. 6 also shows a set of batteries B subdivided into two groups ofwhich each comprises two battery cells. Each cell has its own inductiveheater winding. The windings 51/52 of one group are connected in seriesto the output of the inverter 55. The windings 53/54 of the other groupare also connected in series to the inverter and consequently inparallel to the windings 51/52.

Particular advantages are afforded by inductive preheating according tothe invention when applied to unfilled, drycharged batteries prior toactivation. It is known that shortly upon activation of dry-chargedbatteries, especially at low temperatures, the high-current capacity isslight. Due to the alternating field of the inductive heating, allelectrode plates of the battery are uniformly preheated. When activatingthe battery, the electrolyte then penetrating into the pores of thelocalities at which the rate-determining reactions of the energyconversion occur, i.e., the boundary faces between electrolyte andactive mass, possess approximately the highest temperatures within thestorage battery so that the power capacity of the battery attains thehighest feasible value.

The inductive heating according to the invention operates with unfilledstorage batteries with the same good efficiency as with filledbatteries. In contrast thereto, the heating performance with theabove-mentioned heating methods heretoat unfilled batteries because theheat transfer between the inner wall of the block container and theplate is bad due to the absence of the electrolyte. The knownalternating-current heating is completely impossible with unfilledbatteries because in this condition the battery cannot receive anycurrent so that no heat losses can occur within the interior of thebattery.

To those skilled in the art, it will be obvious upon a study of thisdisclosure that our invention permits of various modificaclaims annexedhereto.

We claim:

1. The method of heating storage batteries having parallel electrodeplates, such as lead-acid batteries, which comprises duced therein bythe field.

2. The method according to claim 1, wherein the inductive alternatingfield has a frequency of at least about 250 Hz.

3. The method according to claim 1, wherein the inductive alternatingfield has a frequency in the range from about 250 Hz to about 1,500 Hz.

4. The method according to claim 1 which comprises reducing theintensity of the alternating field with rising temperature of thebattery.

5. The method according to claim 1 which comprises changing thefrequency of the alternating field during the heating period.

6. The method according to claim 1 which comprises sensing thetemperature in the storage battery, and controlling the intensity of thealternating field independence upon the change in the temperaturesensed.

7. The method according to claim 1 wherein said battery current, andwhich comprises supplying said inductive alternating field with heatingpower from said alternator by tapping said power off the output of saidalternator ahead of said diodes.

and which comprises connecting said windings in a cyclical three-phasecircuit with each other to the three phases of said alternator.

10. The method according to claim 1 wherein a group of said batterieshas respective induction heater windings energized from a direct-currentline through a direct-current to alternating-current converter, andwhich comprises connecting said windings in series-parallel connectionto said converter.

11. The method according to claim 1 wherein said field is produced by aninduction winding and which comprises connecting a capacitance forcontrolling the reactive impedance and power consumption.

12. Device for heating storage batteries, such as lead-acid batteries,comprising holder means, a battery having electrode plates and beingmounted in said holder means when the battery heating device is inoperation, electric induction winding ing-current energizing circuit,said winding means being situated on said holder means in surroundingrelation to the battery electrode plates with the field-line directionpassing through the respective planes of the plates to induce electricshort-circuit currents in the electrode plates.

13. Device according to claim 12, wherein said induction winding meanscomprise a coil having winding turns extending v substantially in aplane parallel to that of the electrode plates.

14. In a device according to claim 12, said holder means comprising astorage-battery container structure, said induction winding means beingembedded within the walls of said container structure.

15. In a device according to claim 14, said container structurecomprising a vessel which forms part of the storage battrated windingsat the edges of said covers.

16. Device according to claim 15, comprising flux-guide sheet membersdisposed on said distributed windings at said side walls ofsaid vessel.

space, and a heat insulation filling said space.

19. In a device according to claim 18, said box being formed ofglass-fiber-reinforced plastic.

20. In a device according to claim 14, said container structurecomprising an inner vessel ducting material.

filling the

1. The method of heating storage batteries having parallel electrodeplates, such as lead-acid batteries, which comprises subjecting theelectrode plates of the battery to an inductive alternating magneticfield oriented relative to the battery so as to have the field directionpass through the respective planes of the plates thus heating the platesby electric current induced therein by the field.
 2. The methodaccording to claim 1, wherein the inductive alternating field has afrequency of at least about 250 Hz.
 3. The method according to claim 1,wherein the inductive alternating field has a frequency in the rangefrom about 250 Hz to about 1,500 Hz.
 4. The method according to claim 1which comprises reducing the intensity of the alternating field withrising temperature of the battery.
 5. The method according to claim 1which comprises changing the frequency of the alternating field duringthe heating period.
 6. The method according to claim 1 which comprisessensing the temperature in the storage battery, and controlling theintensity of the alternating field in dependence upon the change in thetemperature sensed.
 7. The method according to claim 1 wherein saidbattery forms part of an electric power plant having an alternator andrectifier diodes connected to the alternator to provide direct current,and which comprises supplying said inductive alternating field withheating power from said alternator by tapping said power off the outputof said alternator ahead of said diodes.
 8. The method according toclaim 1 for heating a battery on a vehicle having a direct-currentsupply, which comprises converting direct current from said supply toalternating current, and energizing said inductive field by saidconverted current.
 9. The method according to claim 1 wherein a group ofsaid batteries has respective induction heater wIndings energized from athree-phase alternator and which comprises connecting said windings in acyclical three-phase circuit with each other to the three phases of saidalternator.
 10. The method according to claim 1 wherein a group of saidbatteries has respective induction heater windings energized from adirect-current line through a direct-current to alternating-currentconverter, and which comprises connecting said windings inseries-parallel connection to said converter.
 11. The method accordingto claim 1 wherein said field is produced by an induction winding andwhich comprises connecting a capacitance for controlling the reactiveimpedance and power consumption.
 12. Device for heating storagebatteries, such as lead-acid batteries, comprising holder means, abattery having electrode plates and being mounted in said holder meanswhen the battery heating device is in operation, electric inductionwinding means joined with said holder means and having analternating-current energizing circuit, said winding means beingsituated on said holder means in surrounding relation to the batteryelectrode plates with the field-line direction passing through therespective planes of the plates to induce electric short-circuitcurrents in the electrode plates.
 13. Device according to claim 12,wherein said induction winding means comprise a coil having windingturns extending substantially in a plane parallel to that of theelectrode plates.
 14. In a device according to claim 12, said holdermeans comprising a storage-battery container structure, said inductionwinding means being embedded within the walls of said containerstructure.
 15. In a device according to claim 14, said containerstructure comprising a vessel which forms part of the storage batteryproper and has a bottom and side walls, and a cover on top of saidvessel, said induction winding means comprising a distributed windingextending at said bottom and side walls, a concentrated winding at thetop edges of said vessel, another distributed winding on the surface ofsaid cover, and concentrated windings at the edges of said covers. 16.Device according to claim 15, comprising flux-guide sheet membersdisposed on said distributed windings at said side walls of said vessel.17. Device according to claim 16, wherein said flux-guide sheet membersare arranged about midway along the height of said vessel and haveapproximately the same vertical dimension as the electrode plates. 18.In a device according to claim 14, said container structure comprising avessel which forms part of the storage battery proper and has a bottomand side walls, and a cover on top of said vessel, said inductionwinding means comprising winding turns located at said bottom and sidewalls and further winding turns on said cover, a synthetic plasticembedment which fixed said respective winding turns to said vessel, abox surrounding said vessel and forming therewith an interstitial space,and a heat insulation filling said space.
 19. In a device according toclaim 18, said box being formed of glass-fiber-reinforced plastic. 20.In a device according to claim 14, said container structure comprisingan inner vessel which forms part of the battery proper and an outer boxstructure into which said vessel is inserted and which forms therewithan interstitial space, flux-guide sheet members surrounding said windingmeans, said winding means and said members being disposed in the regionsituated between the outer confines of said box and vessel respectively,and heat-insulating foam material filling the voids remaining in saidinterstitial space.
 21. Device according to claim 18 wherein said boxhas an outer wall surface formed substantially of metal.
 22. Deviceaccording to claim 18 wherein said box has an outer wall surface formedsubstantially of magnetically conducting material.